Humidity measurements which indicate the humidity content of air are usually carried out with the aid of a capacitive humidity sensor. To determine the humidity in the air, the capacitance of the humidity sensor is ascertained at least relative to a reference capacitance and assigned to a humidity value.
A circuit system for measuring the humidity with the aid of a capacitive humidity sensor and with the aid of a microcontroller is discussed in U.S. Pat. No. 7,084,644 B2. To measure the humidity, the humidity sensor is repeatedly charged and discharged into a charge storage element and retrieved when the voltage across the charge storage element reaches or exceeds a threshold value. The number of discharging processes then represents a degree of the capacitance of the humidity sensor. To be able to carry out the discharging processes of the humidity sensor without discharging the charge storage element, a protective diode or a switch is provided, which disconnects the humidity sensor from the charge storage element at the point in time that the humidity sensor is charged.